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TT: Fachverband Tiefe Temperaturen

TT 8: Superconductivity - Poster Session

TT 8.31: Poster

Monday, March 26, 2007, 14:00–17:45, Poster A

Josephson π-junctions and their application in superconducting flux qubits — •Georg Wild, Achim Marx, and Rudolf Gross — Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, 85748 Garching, Germany

Superconducting flux qubits suffer from the need of a flux bias, which has to be extremely stable in time. This problem can be circumvented by inserting an additional π-phase shift element in the qubit ring, which formally replaces this flux bias. A phase shift of π between the phases of two superconductors (S) is provided by a Josephson junction (JJ), where the weak coupling is established by a thin ferromagnetic metal layer (F) of appropriate thickness. For applications in quantum circuits, where damping and decoherence has to be minimized, an insulating layer (I) is needed to increase the quality factor of the junction. For the realization of flux qubits with π-phase shift elements we have developed an in-situ self-aligned multilayer process to realize SIFS-JJ. Our junctions show RCSJ-like current-voltage characteristics and a Fraunhofer pattern like modulation of the critical current with magnetic field. The dependence of the I_c R_n-product on the ferromagnet thickness shows a crossover between the zero- and the π-state.
This work was supported by the DFG via SFB 631.